High-frequency modulating system



Sept. 27, 1949.

w. w. HANSEN ET AL HIGH-FREQUENCY MODULATING SYSTEM Filed Dec. 50, 1942 4 Sheets-Sheet 1 -INVENTORS:

. W W- HAN SEN R. H. VARIAN PMB' ATTORNEY Sept. 27, 1949.

w. w. HANSEN ETAL 2,482,766 HIGH-FREQUENCY MODULATING SYSTEM Filed D80. 50, 1942 4 Sheets-Sheet 2 INVENTORS: W. W. HANSEN BY R. H. VARIAN ATTORNEY p 7, w. w. HANSEN ETAL 2,482,766

FIG. l0

HIGH-FREQUENCY MODULATING SYSTEM Filed Dec. 30, 1942 4 Sheets-Sheet 3 luvi-zr rro's W. W. HAN 5E N R. H. VARIAN BYWMQM ATTORNEY p 1949- w. w. HANSEN ETAL HIGH-FREQUENCY MODULATING SYSTEM Filed Dec. 30, 1942 4 Shqets-Sheet 4 HI I MH- m: OE

INVENTORS W. W. HANSEN BY R. H, VARIAN Wad/43 M ATTORNEY a ed Sept. 27, 1949 essence HIGmFnEQUENoY Monum'rmo srsrm William W.

Vaifian, Wantagh, N. Y., ass

Hansen, Garden City, and Russell H.

ignore to The Sperry Qorporation, a corporation ofDelawa're Application December 30, 1942, Serial No. 470,678 InGreatBritainJuly 1,1942 1 a '34 Claims. (01. sat-'11) 1 This invention relates, generally, to the control of ultra high frequency electron beam velocity modulating tubes of the type disclosed in U. S.

space due to changes in acceleration voltage must be accompanied by a change in the phase angle between "buncher" and "catcher" resonators.

Patent No. 2,242,249, entitled Electrical converter, issued May 20, 1941, in the names of Sigurd F. Varian and William W. Hansen, and, more specifically, to novel modulation means by which pure amplitude or frequency modulation can be obtained using such velocity modulation tubes.

This application is a continuation-in-part of copending application Serial No. 420,770, entitled Electronic tuning control," filed November 28, 1941, and now U.- S. Patent No. 2,439,387, issued April 13, 1948'. Part of the subject matter of invention shown in this application is also shown and claimed in two copending divisional applications in the names of the same inventors, one of which is application Serial No. 584,660, entitled High-frequency modulating system," filed March 24, 1945, and the other is application Serial No. 586,007, entitled High-frequency modulating system, filed March 31, 1945.

As is shown in U. S. Patent No. 2,281,935, entitled Modulation system, issued May 5, 1942, in the names of Russell H. Varian and William W. Hansen, electron beam velocity modulating tubes may have their carrier outputs modulated by signal frequencies. The most generally employed methods of modulation have been either to insert the signal voltage in series with the beam acceleration voltage or to supply the signal voltage to a fine wire mesh control grid interposed between the cathode and the entrance grid of the first resonator of the tube. If the action takes place in an oscillator tube, frequency as well as amplitude modulation will result.

One cause of frequency modulation depends on the well known fact that a space filled with electrons has a dielectric constant which differs from the dielectric constant of free space. A variation of the electron beam current by a signal voltage on the control grid alters the dielectric constant of the resonators through which the beam passes thus changing the effective tuning capacity and introducing a frequency change. A second source of frequency modulation lies in the change of phase between the driving voltage and the feedback voltage when the beam velocity is altered by a signal voltage in series with the.

beam acceleration voltage. The condition that oscillation occurs when the phase angle around the complete regenerative circuit is equal to some integral number times 21- radians indicates that any change in the transit time in the bunching This implies a. frequency change accompanying the change in acceleration voltage. It is to be understoodthat frequency modulation will not occur in a modulated amplifier which is isolated from the oscillator by a buifer resonator. This procedure is, however, often undesirable since three more resonators are added which complicate the apparatus and greatly increase the tuning problem.

On the other hand, under some circumstances,

' due to the sharpness of the resonance curves of the resonators themselves, it is diflicult to produce a pure frequency modulated carrier without simultaneous amplitude modulation.

It has been disclosed in above-mentioned Patent No. 2,281,935 that pure amplitude modulation or pure frequency modulation may be obtained by using combinations of acceleration voltage modulation and beam current modulation of the proper amount and in the correct phase relationship. This has the disadvantage, however, that acceleration voltage modulation requires a large signal amplitude and abstracts power from the signal source.

It is, therefore, the principal object of the present invention to provide means for obtaining, as desired, either amplitude or frequency modulation in ultra high frequency oscillators of. the electron beam velocity modulating type without the simultaneous occurrence of the undesired form of modulation. I

Another object is to provide means for obtaining pure amplitude or pure frequency modulation with moderate amplitude signals and negligible signal power consumption by impressing the signal upon the control grids of a plurality of electron beams coacting with coupled electromagnetic fields.

Still another object is to modify the modulation characteristics of an electron beam velocity modulating tube by altering the dielectric constant within one or more resonators of the device with one or more auxiliary electron beams.

A further object of the present invention lies in the provision in an ultra high frequency electron beam velocity modulating tubeof an auxiliary electron beam or beams adapted to maintain the average electron density within common resonator or resonators substantially constant when the average electron density of the main electron beam is modulated by a signal voltage.

A still further object lies in the provision in an ultra. high frequency electron beam velocity modulating tube of an auxiliary beam or beams adapted to vary the average electron density within a common resonator or resonators at a signal frequency while the average electron density of the main electron beam remains substantially constant.

Yet another object is to provide means for obtaining frequency modulation without simultaneous amplitude modulation in an ultra high frequency electron beam velocity modulating device comprising means for creating and controlling a pair of auxiliary electron beams whose intensity is varied in accordance with a signal voltage while the electron groupings of the auxiliary beams are maintained inphase opposition with each other, thus substantially cancelling the effect of the auxiliary beams on the high frequency. field but serving to vary the average electron density within a common resonator or resonators at the signal frequency.

Another object is to provide means in an ultra high frequency tube of the character described for selectively obtaining either pure amplitude modulation or pure frequency'modulatlon by a simple operational adjustment.

Still another object is to provide means for producing amplitude modulation without simultaneous frequency modulation in an ultra high frequency electron beam velocity modulating device, comprising means for creating and controlling a pair of auxiliary electron beams whose intensity is varied in accordance with a signal voltage in predetermined phase relation with respect to the intensity variation of the main electron beamwhile the electron groupings of the auxiliary beams are maintained in phase opposition with each other, thus substantially cancelling the effect of the auxiliary beams on the high frequency field but serving to maintain the average electron density within a common resonator or resonators substantially constant.

Yet a further object is to provide, in an electron beam velocity modulating oscillator having a cavity resonator, means for controlling the average electron density within the resonator in accordance with a signal wave either to produce or to compensate for changes in the resonant frequency of the oscillator without imparting energy to the high frequency field therein comprising means for projecting an electron beam through the high frequency field of the resonator, and grid means'for controlling the beam current, the beam being so directed as to be collected by the side of the resonator or other collector means without providing feedback coupling with the field.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is a longitudinal section view of a novel multi-beam two resonator form of the modulatoroscillator of the present invention taken along cutting plane line l-l of Fig. 2.

Fig. 2 is a cross-section of the structure of Fig. 1 taken along the cutting plane line if-2 of Fig. 1.

Fig. 3 is a longitudinal section of an alternative form of the modulator-oscillator of the present invention taken along cutting plane line 33 of Fig. 4.

Fig. 4 is a cross-section of the structure of Fig. 3 taken along the cutting plane line 4 -4 of Fig. 3. Fig. 5 is a schematic wiring diagram of the device illustrated in Fig. 1.

Fig. 6 is a schematic wiring diagram of a single resonator or reflex type of multi-beam modulator-oscillator.

Fig. '7 is a schematic wiring diagram of the device shown in Fig. 3.

Fig. 8 is a schematic wiring diagram of an alternative form of reflex type of multi-beam modulator-oscillator.

Fig. 9 is a schematic wiring diagram of a modification of the device shown in Fig. 6.

Fig. 10 is a schematic wiring diagram of an alternative form of two-resonator modulatoroscillator.

Fig. 11 is a schematic wiring diagram of an embodiment of the invention employing electronic tuning means in the feedback coupling between resonators of conventional two-resonator electron beam velocity modulating tube.

Fig. 12 is a schematic wiring diagram of a modification of the device shown in Fig. 9.

Fig. 13 is a schematic wiring diagram of a modification of the device shown in Fig. 7.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

It has been demonstrated mathematically and verified experimentally that the presence of free electrons within an electric field may either increase or decrease the dielectric constant of the space containing these charges from the unity value of a pure vacuum. For example, it is observed in the study of the ionosphere that the dielectric constant may be reduced to zero and even reversed in sign by the action of the electrons.

r The effect is mathematically very complex but it is a function, among others, of the electron density, the frequency of the electric field, and the transit time of the electrons passing through the field. In general, it may be said that if the electrons are projected in a low velocity beam and remain within the electric field for a duration long compared to a cycle of the field frequency, the dielectric constant is decreased by their presence. Contrarily, electrons projected through the electric field at a high velocity in a time short compared to a cycle of the field frequency cause an increase in the dielectric constant. The ionosphere ,exhibits the former effect while most electron velocity modulating devices exhibit the latter effect since electrons remain in the impressed electric fields for long and short durations, respectively. In the present invention both modes of operation are contemplated, and therefore, operating conditions stated for explanatory purposes are not to be considered in any way to limit the device to the exclusive employment of either high or low velocity electron beams. Referring now to Fig. 1, there is shown a tworesonator velocity modulation tube of the type disclosed in copending application Serial No. 451,796, entitled High-frequency tube structure," and filed July 21, 1942, in the name of William W. Hansen, in which a plurality of electron beams are projected through a plurality of reentrant poles containing grids and spaced symmetrically within the resonators. The multi-beam tubes described in the aforementioned application were utilized as frequency shifters or as balanced modulators, but in the present invention they are adapted to produce pure amplitude or pure frequency modulation of the ultra high frequency carrier.

The device illustrated in Fig. 1 is provided with a buncher resonator 60 and a "catcher resonator 6| connected by three symmetrically spaced drift tubes 41, 48 and 46. Drift tubes 41, 46 and 49 provide reentrant members 62, 63 and 64, respectively, in resonator 66 and similar members 62', 63, and 64 in resonater 6 Tube 41 is shielded by an exit grid 46 of resonator 66 and by an entrance grid 56 of resonator 6| to form a substantially field free space. Tubes 48 and 49 are of similar construction. Fig. 2 shows the placement of the drift tubes relative to the resonator 66. Resonator 66 has entrance grids 45, 5'! and 58 placed opposite the reentrant members 62, 63 and 64, respectively, while resonator 6| has an exit grid 5| positioned opposite member 62' and similar grids opposite members 63' and 64'. Electron emissive cathodes 65, 66 and B1 are placed in line with entrance grids 45, 51 and 58, respectively, while control grids 52, 55 and 56, respectively, are interposed between these cathodes and their respective entrance grids. Supports for the cathode and grid structures are not shown for the sake of simplicity in the drawing since they are well known to the art. Coupling loop 4| in resonator 6| and loop in resonator 66 are interconnected by coaxial line 42 to provide a feedback path between th resonators.

The operation of Fig. 1 may be more clearly understood with reference to Fig. 5. Electrons emitted from cathode 65 are accelerated by the voltage of a batter I6I placed between this cathode and entrance grid and are projected through this grid. In the space between grids 45 and 46, the electrons are velocity modulated by an ultra high frequency electric field existing in the buncher resonator 66. The electrons pass through exit grid 46 down the drift tube 41 and arrive between grids 56 and 5| at a time when the velocity modulation has resulted in density modulation or grouping of the electrons. The arrivals of these bunches of electrons impart energy to anultra high frequency electric field contained in the "catcher resonator 6|. A portion of the energy is fed back to resonator 66 by means of the coupling line 42, and thus the electromagnetic oscillations are maintained in a well known manner. The average intensity of the electron beam and therefore the amplitude of oscillation may be adjusted by potentiometer I64 supplying a bias voltage to the control grid 52.

Cathodes 66 and 61 provide electron beams which are also accelerated through resonator 66, drift tubes 48 and 49, respectively, and resonator 6|. Voltage from a battery I62 in series with battery Iill is applied to cathode 66 while a po-' tential from the series combination of abattery I63 and the batteries I6I and I62 is impressed on cathode 61. The difference between the acceleration voltages is such that the density groupings of these beams arrive at resonator 6| in phase opposition with each other, resulting in no contribution of energy to the high frequency field contained therein although these beams unavoidably remove some energy from resonator 66. Potentiometers I65 and I66 supply biasing voltages to grids and 56,- respectively, and are adjusted to maintain average electron currents from cathodes 66 and 61 preferably equal to each other and substantially one-half the intensity of the beam from cathode 65.

A signal source I6! is connected to the primary of an isolation transformer I68 whose secondary is center-tapped to ground and whose output terminals are loaded by potentiometers I69 and H6. Sliding contact I I of potentiometer H6 is coupled through a blocking condenser to the grid 52 while a sliding contact I I2 of the potentiometer 6 I69 is connected by blocking condensers to grids 55 and 56.

Substantially pure amplitude modulation may be obtained from the device of Fig. 5 by adjusting the contact II2 to tap off modulation voltage for grids 55 and 56 approximately one-half the amplitude of and in reverse phase to the signal applied to grid 52. The average electron density of the three beams passing through resonators 66 and 6| is thus maintained substantially constant; consequently no frequency modulation due to the varying electrons density 0f the exciting beam from cathode 65 is produced. Since the amplitude of the high frequency field is essentially determined by the intensity of the exciting beam, the amplitude of the output wave supplied to coaxial line 39 is modulated substantially independently of the auxiliary beams. It is to be understood that the auxiliary beams from cathodes 66 and 61 need not be one-half the intensity of the exciting beam since the contact II2 may be empirically adjusted to obtain minimum frequency swing. While it is often desirable to employ low intensity auxiliary beams to avoid loading the resonators, it seems obvious that there are an unlimited number of adjustments of the intensity and degree of modulation of the auxiliary beams which will substantially neutralize the resonator detuning caused by the signal frequency variation of the exciting beam.

Substantially pure frequency modulation may also be obtained from the device of Fig. 5 by placing the tap I I I at the center of potentiometer II6 which corresponds to ground potential and impressing a full signal upon the control grids 55 and 56 of theauxiliary beams. conditions, the resonant frequency of the oscillator is varied at the signal frequency without variation of the exciting beam intensity. In this manner, substantially no amplitude modulation is impressed upon the output wave. Predetermined amounts of amplitude and frequency modulation may, of course, be obtained by adjusting the signal voltages on grids 52, 55 and 56 to intermediate values.

The present invention may with equal ease be embodied in a form of single resonator modulator oscillator of the general type disclosed in U. S. Patent No. 2,250,511, entitled Oscillator stabilization system, issued Jul 29, 1941,.in the names of Russell H. Varian and William W. Hansen. Referring to Fig. 6, there is seen a reflex type of electron beam" velocity modulating device that has a single resonator H3 which acts to both bunch and catch electron beams projected therethrough. Cathodes H4, H5 and H6 emit electron beams which are projected through the resonator H3 by accelerating voltages supplied from batteries |6I, I62 and I63 connected in a manner similar to their unprimed counterparts in Fig. 5. Reflector plates H1, H8 and H9, maintained at an appropriate potential by a tap on the battery I 6|, are adapted to return the beams to resonator II 3 after the velocity modulation of the electrons suffered by their initial passage through the resonator has resulted in density modulation of the beams.

Because of the difference in acceleration potentials, the electron groupings of the beams from cathodes H5, H6 are in out of phase relation upon their second arrivals within the resonator H3, and therefore these beams contribute no energy to the ultra high frequency field contained therein. The beam from cathode II4 alone excites the resonator II3. Control grids Under these I2I, I22 and I23 are placed before the cathodes H4, H and H8, respectively, and it seems evident that signal voltages of proper magnitude and phase may be impressed upon these grids according to the teachings of Fig. 5 to obtain either pureamplitude modulation, pure frequency modulation, or calculable amounts of both types.

Referring now to Fig. 3 there is shown a type of two-resonator tube disclosed in above-mentioned copending application Serial No. 420,770 of which the present application is a continuation-ln-part. As therein shown, the device comprises buncher and catcher resonators 99 and 9|, respectively, containing reentrant members 92, 93 and 92', 93', respectively. The reentrant members 92 and 92' are formed by continuations of a drift tube 94 while members 93 and 93 are portions of a tube 95. The symmetrical placement of the tubes within the resonators is shown by the cross-section view of Fig. 4. A cathode 96 is placed in line with the drift tube 94 to enable an electron beam to be projected through the usual grid-shielded apertures in resonator 90 within which the beam is velocity modulated and thence supplied to resonator 9| which the beam excites in the conventional manner. Oscillation is sustained by positive feedback between resonators 9| and 90 consisting of a coaxial lead I6 attached to coupling loops I4 and I5 which couple to the fields of resonators 90 and 9|, respectively. A coupling loop I2 and connected coaxial line I3 may be used to supply ultra high frequency power to utilization apparatus. A control grid 68 is interposed between cathode 96 and resonator 90, the conventional use of which as a modulation electrode gives rise to a mixture of amplitude and frequency modulation. The following means are provided to enable the modulation characteristics of the device to be altered at will.

Above resonator 90 is placed a cathode"I8 before an entrance grid 88 lying opposite reentrant member 93. Likewise, below resona or 9| is placed a cathode I9 in front of an entrance grid 8| placed opposite reentrant member 93'. Positioned between cathode I8 and entrance grid 88 and between cathode I9 and entrance grid 8| are control grids 82 and 83, respectively. Tube 95 is divided by a transverse wall 91 which is adapted to collect and dissipate the energy of the electrons emitted by cathodes I8 and I9.

The operation of the device shown in Fig. 3 may be more clearly understood with reference to Fig. '7. A potential source I25, connected to the cathode 96, accelerates the exciting electron beam whose average intensity is adjusted by a variable bias voltage on the control grid 68 obtained from a potentiometer I26 in series with a grid load resistor I21 placed across the voltage source I25. Electron beams from cathodes I8 and I9 are likewise accelerated by a battery I28 across which is connected a potentiometer I29 in series with a grid load resistor I3I. Control grids 82 and 83 are maintained at a desired bias voltage by the potentiometer I29. Since the electron beams from cathodes I8 and I9 do not couple with both resonators but are collected on wall 91 after only a single passage through a single resonator, they cannot contribute to the ultra high frequency field though they load the resonators slightly and alter their resonant frequency. Tap III on potentiometer IIIl supplies the signal voltage to grid 68 while tap M2 on potentiometer I99 supplies the signal voltage to grids 82 and 83.

Substantially pure amplitude or pure frequency modulation may be obtained from the device shown in Fig. '7. A signal wave may be readily impressed on the grids 82 and 93 with an amplitude and phase such that the electron beams from cathodes I8 and I9, respectively, alter the resonant frequency of resonators 90 and 9|, respectively, in an opposite direction to the detuning of these resonators by the modulated exciting electron beam and to a substantially equal extent. If the velocities of the exciting and auxiliary beams are greatly different, like changes in beam intensities may have opposite effects on the dielectric constant of the resonators as mentioned above. tions the modulating and corrective signal waves are impressed on the control grids in like phase in order to cancel frequency modulation. Substantially pure frequency modulation, on the other hand, may be obtained by removing the signal wave from grid 68. If desired, either one of the auxiliary beams may be eliminated and the frequency control accomplished solely in one resonator.

Referring now to Fig. 8, there is seen a type of reflex electron beam velocity modulating tube of the type shown in U. S. Patent No. 2,250,511 but having a transverse electron control beam similar to that disclosed in above-mentioned copending application Serial No. 420,770. The device oomprises an electron emissive cathode I35 from which an electron beam is accelerated by the potential from a battery I36 through a mesh control grid I31 and thence through a resonator I38 having entrance and exit grids I39 and MI, respectively. Behind exit grid MI is mounted a reflector plate I42 supplied with a voltage from a tap on the battery I38. The electron beam is reflected back into the resonator I38 where it maintains an ultra high frequency field in the well known manner. A coaxial line I43 attached to a coupling loop I44 is adapted to remove energy from the resonator I38.

Attached to the side of resonator I38 is a means for producing an electron beam transverse to the electric field of theresonator. A cathode I46 of this device produces an electron beam which is accelerated through a mesh control grid I41 and through a grid I48 in the side wall of resonator I38 by a voltage supplied by a battery I49, so that the beam passes substantially at right angles to the electron beam from cathode I35 and between resonator grids I39, I4 I, preferably without impinging on these latter grids or the resonator walls. Loop I44 and line I43 are shown in the plane of the paper for convenience in drawing, but would preferably be located so that the beam from cathode I46 would not strike them. The modulation control grids I31 and I" are connected to the taps III and H2, respectively, of the potentiometers III) and I09, respectively.

In operation, the beam from cathode I46 contributes no energy to aid in maintaining the oscillating electromagnetic field within the resonator; in fact, it unavoidably extracts a small amount of energy. If the beam current intensity from cathode I35 is increased, there results an increase in the amplitude of oscillation of the electromagnetic field and a decrease in its frequency as a consequence of the tuning effect on the resonator. An increase in the beam current from cathode I46, however, produces a decrease Under these conditherefore supplies no energy to the ultra in output, dueito its effect in loading the resonator, as wellas a decrease or increase in output frequency dependent upon'whether the control beam has a positive or negative effect on the dielectric'constant of the resonator. Predetermined amounts of amplitude and' frequency modulation may be obtained, therefore, by the amplitudte and phase adjustment of the signal voltages on the control grids I 81 and I 41.

Fig. 9 illustrates an alternate form 01' themesent invention wherein a reflex typeof ultra high frequency oscillator has an auxiliary electron beam projected at preferably a low velocity parallel to the exciting electron beam. A resonator I5I of the device of Fig. 9 has across-section similar to that shown in Fig. 4. Cathode I52 provides an electron beam whose intensity is controlled by a grid I53 and which is accelerated by a battery I54 through entrance and exit grids I58 in the resonator I5I. A reflector electrode from a cathode I83 is projected through the resonator I82 for tuning purposes only. A control grid I84 placed before cathode I83 is adapted I55 maintained at an appropriatevoltage by a tap on the battery I 54 returns the beam to the resonator I5I which is excited therebyin the usual manner. Cathode I56 emits electrons which are projected by the acceleration voltage of a battery I6I- past control grid I51, and through a second pair of entrance and exit grids I58 in the resonator I5I. The beam from cathode I56 is dissipated by a collector electrode I62 and high frequency field. Grids I 53 and I51 are coupled to the signal source I01 by means of taps I II and II 2, respectively, of the potentiometers H0 and I09, respectively. The modulation characteristics of this device may be altered in a similar manner to the devices previously discussed.

Fig. 10 shows a form of the invention in which auxiliary electron beams are provided in a tworesonator device projecting substantially transversely of the electric fields in resonators. A cathode I63 emits an electron beam which is employed to excite resonators I64 and I 65 in the well known manner. Cathodes I66 and I68 provide electron beams in resonators I64 and I65, respectively, which pass transversely between the grid structures I68 and I69, respectively, and thus. contribute no energy to these resonators. Grids I1I, I12, I13 are positioned before cathodes I63, I66, and I61, respectively, to control the intensities of the respective beams. Grids HI and I12 are coupled to taps III and H2, re-

to control the beam intensity and thus the resonant frequency of the resonator I8I. It seems evident that an ultra high frequency field will be set up in resonator I8I when tube I15 is excited by anlelectron beam from cathode I85. A control grid I86 may be employed to modulate the electron beam from cathode I85 with a signal from source I01 while the beam from :athode I83 maybe likewise modulated by the same signal adjusted as desired in amplitude and phase with respect to the first-mentioned modulating voltage. An alteration of the resonant frequency of resonator I8I effects a change in the frequency of oscillation of the tube I15 dependent upon the coupling'coeflicients between resonator I8I and resonators I18 and I19 and the efllciencles of the resonators. The structure of Fig.-11 may thus be'utilized in a manner similar to the previously discussed devices to produce any desired amount of types of modulation. Resonator I BI is illustrated as reentrant, but it is to be understood that this resonator may have other forms. For example, resonator I8I may bea non-reentrant cylinder excited at its fundamental mode with the electric field parallel to the axis'of symmetry. A high intensity low velocity electron beam may be projected across the cylinder perpendicular to the electric field for tuning purposes. This produces a high efiiciency resonator from which the tuning electron beam abstracts little energy especially if the transit time across the resonator is large compared to he periodicity of the electromagnetic field.

Fig. 12 illustrates a modification of the device Y shownin Fig." 9 wherein the resonator I5I is separated into a driving resonator I5I and a tuning resonator I5I" coupled by a coaxial line I81. Resonator I5I, which may be similar to the resonators discussed with reference to Fig.

,11, couples an impedance to resonator I5I in a.

spectively, of potentiometers H0 and I09, respecvelocities the signal waves. on the control grids .may be adjusted to obtain a minimum of undesired modulation of the generated ultra high frequency wave. Either of the auxiliary beams may be dispensed with if a reduction in the extent of frequency compensation or frequency modulation is immaterial.

Fig. 11 illustrates means for obtaining either pure amplitude or pure frequency modulation from a conventional two-resonator electron beam velocity modulating tube I15. Device I15 has feedback coupling means comprising coaxial lines I16 and I11 individually coupled tocatcher and buncher resonators I18 and'l19, respectively, of tube I15 and having common coupling with a resonator I8I. Resonator I8I is a portion of an electronic tuning device I82 of the general type disclosed in above-mentioned application Serial No. 420,770. An electron beam manner analogous to simple coupled circuits.

The operation of the device shown in Fig. 12 is similar to that of Fig. 9 and consequently needs no special explanation. v

Fig. 13 illustrates a conventional two-resonator electron beam velocity modulating device I88 having a buncher resonator I89 and a catcher resonator I9 I to which are coupled by coaxial lines I94 and I electronically tuned resonators I92 and I93, respectively. Resonators I92 and I93 have electron beams which may be modulated to vary the impedances coupled to resonators I89 and I9I, respectively, thus altering the modulation characteristics of the device I88. If desired, one of the electronic tuning controls I92, I93 may be eliminated and all control effected with a single resonator.

It appears obvious that the teachings of the present invention may be extended to other types of electron beam velocity modulation devices that have radial shooting exciting beams, annular resonators, and similar structural modifications. The usual tuning arrangements may in employed with the illustrated embodiments of the present invention. Great latitude may be exercised in design of resonators, use of smoothing grids, employment of collector electrodes for mixer operation, and in similar engineering decisions.

As many changes could be made in the above construction and many apparently widely difeither or both quency modulation incurred ferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A method of producing desired relative amounts of amplitude and frequency modulation simultaneously in an electron beam velocity modulating device ranging from substantially pure amplitude modulation to substantially pure frequency modulation, comprising the steps of pro-' jecting a plurality of electron beams through an electromagnetic field, at least one beam for maintaining the field and at least one beam for tuning purposes only, and varying the intensities of all said electron beams in accordance with the same signal waves with an amplitude and phase relationship correlated to the desired relative amounts of amplitude and frequency modulation of the electromagnetic field.

2. A method of producing desired relative amounts of amplitude and frequency modulation simultaneously in an electron beam velocity modulating device ranging from substantially pure amplitude modulation to substantially pure frequency modulation, comprising the steps of exciting an ultra high frequency electromagnetic field in said device by projecting an exciting electron beam therethrough, projecting an auxiliary electron beam solely for tuning least a portion of the electromagnetic field created by said exciting electron beam, and modulating the intensities of both the electron beams in accordance with the same signal waves with an amplitude and phase relationship correlated to the desired relative amounts of amplitude and frequency modulation of the electromagnetic field.

3. A method of producing desired relative amounts of amplitude and frequency modulation simultaneously in an electron beam velocity modulating device ranging from substantially pure amplitude modulation to substantially pure frequency modulation, comprising the steps of producing an electromagnetic field by an electron beam, producing an auxiliary electron beam coupurposes through at r 6. A method of obtaining substantially pure amplitude modulation in an electron beam velocity modulating tube, comprising the steps of projecting an electron beam through said tube for exciting an oscillating field in the same, modulating the intensity of said-beam in accordance with a signal, and maintaining the average electron density within said field constant to compensate for frequency modulation incurred by said first beam.

'7. An electron beam-velocitymodulating device adapted to produce desired relative amounts of amplitude and frequency modulation comprising coupled resonator means, means for projecting an electron beam-through at least one of said resonator means to excite electromagnetic oscillations within all said resonator means, means in said device for projecting an auxiliary electron beam through at least one of said resonator means to coact with said electromagnetic oscillations without imparting energy to said electromagnetic oscillations, and means for varying the intensities of the electron beams from said several projecting means in accordance with a signal wave, said lastmentioned means including a control electrode along the path of each of said beams and a source of signal wave coupled to all said control electrodes, said last-mentioned means being adapted to control the relative amplitudes and phases of said electrcn beam intensities in correlation with the desired relative amounts of amplitude and frequency modulation.

pled to said field, and controlling said electron beams in accordance with signal waves having amplitude and phase relationships correlated to the desired relative amounts of amplitude and frequency modulation of said field.

4. A method of obtaining substantially pure modulation in an electron beam velocity modulating tube, comprising the steps of projecting an electron beam through said tube for exciting an oscillating 'field in the same, modulating the intensity' of said beam in accordance with a signal, producing a second electron beam coupled to said field, and modulating said second beam to compensate for undesired modulation produced by said first beam.

5. A method of obtaining substantially pure amplitude modulation inan electron beam velocity modulating tube, comprising the steps of projecting an electron beam through the tube for 'exciting an oscillating field in the same, modulating the intensity of said beam in accordance with a signal, projecting a second beam through the field created by the exciting beam, and modulating the intensity of said beam in accordance with said same signal in a phase relation to said first-mentioned modulating process compensating for freby said modulating process.

' ing adapted to control 8. Means for simultaneously producing in an electron beam velocity modulating device desired relative amounts of amplitude and frequency substantially pure amplitude modulationio substantially pure frequency modulation, comprising resonator means, means aligned therewith for projecting electrons through said resonator means to excite electromagnetic oscillations within the same, means for grouping said electrons at a predetermined frequency, auxiliary means also aligned therewith for projecting electrons to coact with the. electromagnetic oscillations without imparting energy thereto, and means for varying the densities of the electrons from said several projecting means in accordance with a signal wave having a frequency substantially lower than said predetermined frequency, said last-mentioned means hethe relative amplitudes and phases of the electron densities in correlation with the desired relative amounts of amplitude and frequency modulation, and including respective control electrodes in the respective paths of said projected electrons, and a source of said signal wave coupled to said control electrodes.

9. Means for simultaneously producing in an electron beam velocity modulating device desired relative amounts of amplitude and frequency modulation ranging from substantially pure amplitude modulation to substantially pure frequency modulation, comprising resonator means, means aligned therewith for projecting an electron beam through said resonator means to excite 'an electromagnetic field within the same, means for grouping said electrons at a predetermined frequency, means aligned therewith for projecting an auxiliary electron beam through at least a portion of the electromagnetic field without imparting energy thereto, and means including a control electrode along the path of each of said beams and a source of signal wave coupled to said control electrodes, for varying the intensities of said electron beams in accordance with said 10. High frequency apparatus comprising a hollow cavity resonator having a plurality of electron-permeable portions, means for producing aligned therewith for projecting a stream of electrons through one of said portions, means for grouping said electrons at a predetermined frequency, means for modulating said oscillations comprising means along the path thereof for con- -10 oscillations in said resonator comprising means trolling said stream in accordance with a modulation signal having a frequency substantiall lower than said predetermined frequenciesfand means for controlling the modulation of said oscillations comprising means aligned therewith for projecting a second stream of electrons through the other of said resonator portions, and means along the path thereof for controlling said second stream by said same signal.

11. Modulation control apparatus comprising resonator means, means for exciting oscillations within said resonator means including means aligned therewith for projecting an electron beam therethrough and means for grouping said electrons at a predetermined frequency, mean for producing an auxiliary electron beam coupled to said oscillations, and means along the paths thereof for controlling said electron beams in accordance with signal Waves to produce desired amounts of different types of modulation of said oscilla-.

tions, said signal waves having a frequency substantially lower than said predetermined frequency.

12. Modulation control apparatus comprising means for producing an electromagnetic field including means for grouping electron at a predetermined frequency and means for projecting said grouped electrons therethrough, means for producing an auxiliary electron beam coupled to said field, means along the path thereof for controlling said first electron beam in accordance with a modulation signal to produce modulation of said field, said modulation signal having a frequency substantially lower than said predetermined frequency, and means for modifying said modulation comprising means along the path thereof for controlling said auxiliary beam by said same modulation signal.

13. Modulation control apparatus comprising means for grouping electrons at a predetermined frequency, means for producing an oscillating electromagnetic field, means for producing modulation of the oscillations of said field in accordance with a modulation signal having a frequency substantially lower than said predetermined frequency, means for producing an electron beam coupled with said field, and means for modifying said modulation comprising means along the path thereof for controlling said beam.

14. An electron velocity modulating vacuum device for producing ultra high frequency oscillations comprisin means for producing a primary electron beam, a buncher resonator, a

catcher resonator, said primary beam producing Q means and said buncher resonator and said catcher resonator being located in axial consecution, means for modulating the intensity of said primary electron beam with a first signal, means in said device for projecting auxiliary elec- 14 tron beams through said buncher and catcher resonators having respective electron groupings phase displaced to substantially cancel energy interchange of the auxiliary beams with the high frequency field, and means along the paths of said auxiliary beams for modulating the intensity of said auxiliary beams with said first signal in opposite phase to the modulation of said primary beam to maintain the average electron density in the resonators substantially constant.

15. An electron velocity modulating vacuum tube for producing ultra high frequency oscillations comprising a buncher resonator, a catcher I resonator, means for projecting a primary electron beam successively through said buncher and catcher resonators, means in said tube for projecting through said resonators auxiliary electron beams having respective electrongroupings mutuall phase displaced to substantially cancel energy interchange of the auxiliary beams with the high frequency field within the catcher resonator,

and means along the paths of said auxiliary beams for modulating the intensity of the auxiliary beams in accordance with a signal, thus varying the resonant frequency of the resonatprs at the signal frequency 16. In an electron beam velocity modulating vacuum tube of the reflex type' having asingle along the beam resonator adapted to both bunch an electron beam projected therethrough and to catch the beam upon bein subsequently reflected back thereto, thereby producing ultra high frequency oscillations, the combination comprising means aligned therewith for projecting auxiliary electron beams through the resonator having electron groupings phase displaced to cancel any substantial energy-interchange f the auxiliary beams with the high frequency field withinthe resonator, and means along the beam paths for varying the intensities of the auxiliary beams in accordance with an alternating signal thus altering the resonant frequency of the resonator at the signal frequency.

17. In an electron beam velocity modulating vacuum tube having a single resonator adapted to both velocity modulate an electron beam projected therethrough and to be electromagnetically excited by the same beam upon subsequent reflection of the latter in density modulated form back thereto, the combination comprising means along the path thereof modulating the intensity of said exciting electron beam with a signal, means aligned therewith for projecting auxiliary beams through the resonator having electron groupings phase displaced to substantially cancel energyinterchange of said auxiliary beams with the high frequency field within the resonator, and means paths for modulating the intensity of said auxiliary beams with said same signal to maintain the average electron density in the resonator substantially constant.

18. In an electron velocity modulating'vacuum tube, buncher and catcher resonators, means intercoupling said buncher and catcher resonators to produce ultra high frequency oscillations, means in said tube for projecting an electron beam through said resonators, means for varying the intensity of said electron beam in accordance vwith a signal, means for projecting an auxiliary electron beam through one of the resonators, and means along the path of said auxiliary beam for varying the intensity of said auxiliary. beam in accordance with said signal to maintain the average electron density in said one resonator substantially constant.

19. In an electron velocity modulating vacuum tube, buncher and catcher resonators coupled to produce ultra high frequency oscillations, means in said tube for projecting an electron beam through said resonators, means along the path of said beam for modulating the intensity of said beam with a signal, and means in said tube for maintaining the average electron density in said resonators substantially constant.

20. In an electron beam velocity modulating vacuum tube having a single resonator adapted to both velocity modulate an electron beam projected therethrough and to be electromagnetically excited by the same beam upon subsequent reflection of the latter in density modulated form back thereto, the combination comprising means along the path thereof for varying the intensity of said exciting electron beam in accordance with a signal, means aligned therewith for projecting an auxiliary electron beam through the resonator, and means along the path thereof for varying the intensity ofsaid auxiliary electron beam in accordance with said same signal to maintainthe average electron density in the resonator substantially constant.

21. Modulation control apparatus comprising means for producing an electromagnetic field, including a hollow cavity resonator, means aligned therewith for projecting an electron beam therethrough, and means along the path thereof for reversing said beam to reenter said resonator;

means for producing an auxiliary electron beam coupled to said field, means along the path thereof for controlling said first electron beam in accordance 'with a modulation signal to produce modulation of said field, and means for modifying said modulation comprising means along the path thereof for controlling said auxiliary beam by said modulation signal.

22. High frequency apparatus comprising a hollow cavity resonator having a plurality of electron permeable portions, means for producing os-. cillations in said resonator comprising means aligned therewith for projecting a stream of electrons through one of said portions and for reversing said stream to reenter said resonator, means for modulating said oscillations comprising means along the path thereof for controlling said stream in accordance with a modulation signal, and means for controlling the modulation of said oscillations, comprising means aligned therewith for projecting a second stream of electrons through the other of said resonator portions, and means along the path thereof for controlling said second stream by said signal.

23. High frequency apparatus, comprising a velocity modulation device having means defining a pair'of spaced electromagnetic field regions and means in said apparatus for projecting a first electron beam successively through said regions; and means for coupling said regions, including a cavity resonator coupled to each of said regions and means in said apparatus for controlling resonant frequency of said cavity resonator, said frequency controlling means including means for projecting a second electron beam within said cavity resonator.

24. Apparatus as in claim 23, further comprising a source of modulation signal, and means coupled to the pathof said second beam for controlling said second beam by said signal to produce modulation of said fields of said regions.

25. Apparatus as in claim 24, further compris-. ing means coupled to the path of said first beam the 16 for additionally controlling said first electron beam in response to said modulation signal.

26. High frequency apparatus comprising a velocity modulation electron discharge device having a cavity resonator, means for grouping electrons at a predetermined frequency, means'for modulating the output of said device in accordance with a modulation signal, having a frequency substantially lower than said predetermined frequency, and means for controlling the modulation of said output, comprising a second cavity resonator coupled to said first resonator, means aligned therewith for projecting a beam of electrons through said second resonator, and means along the path thereof for controlling said beam by said signal.

2'7. High frequency apparatus comprising a pair of hollow cavity resonators, means adjacent one of said resonators for projecting an electron stream successively through said resonators to produce high frequency oscillations in the second resonator thereof, means along the path of said stream for controlling said stream by a modulation signal to produce modulation of said oscillations,.an'd means in said apparatus for controlling the modulation of said oscillations, comprising a further cavity resonator coupled to one of said first named resonators, means coupled to said further cavity resonator for projecting a stream of electrons through said further resonator, and means coupled to the path of said latter stream for controlling said latter stream by said signal.

28. High frequency apparatus as in claim 27, wherein said further cavity resonator is coupled to both said first named resonators.

29. High frequency modulating apparatus/comprising a pair of cavity resonators, means aligned therewith for projecting an electron stream successively in energy-exchanging relation with said resonators, and feedback means coupling said resonators, said feedback means including a third cavity resonator coupled to both of said pair of resonators, means adjacent said third resonator for projecting a second electron stream through said third resonator, and means coupled to the path of said second stream for controlling said second stream in accordance with modulating signals.

30. High frequency modulating apparatus comprising a high frequency oscillator having a cavity resonator and an output coupled to said resonator, and means in said apparatus for frequency modulating said output, comprising a second cavity resonator coupled to said first cavity resonator, means adjacent said second resonator for projecting an electron. stream through said second resonator, and means along the path of said stream for controlling said stream by modulating signals.

31. High frequency modulating apparatus comprising a high frequency oscillator having a cavity resonator and an output coupled to said resonator, and means coupled to said oscillator for modulating said output, comprising a second cavity resonator coupled to said first resonator and means adjacent said second resonator for varying the tuning of said second resonator in accordance with a modulating signal.

32. High frequency apparatus comprising a cavity resonator, means in said apparatus for i passing a fast stream of electrons through said resonator for producing oscillations therein, and means in said apparatus for projecting a relatively slow stream of electrons through said resonator for tuning control, and means adjacent the 17 paths of said. streams controlling both said Streams by a modulating signal.

33. High frequency modulating apparatus comprising meansfor producing modulated ultra high frequency oscillations, said oscillation producing means including a first, cathode, a first modulating grid, 2. buncher resonator and a catcher resonator, all located in axial consecution; a further cavity resonator coupled both to said buncher resonator and said catcher resonator, said further 10 modulation, said modulation producing means comprising a first modulating grid interposed between said first cathode and buncher resonator, a further cavity resonator coupled both to said buncher and catcher resonators, said further cavity resonator having a second cathode and a second modulating grid both aligned therewith,

18 said first and second modulating grids being adapted to be connected to the common modula- REFERENCES CITED The following references are file of this patent:

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